It has been required recently that diesel engines for passenger cars meet various requirements, such as low noise, low fuel consumption, low emissions and high power. The key to improve the noise is to reduce a combustion noise known as “Diesel knock noise”. Conventional approaches to reduce the diesel knock are decreasing combustion excitation force due to pilot/pre fuel injection, adding ribs to engine blocks or improving noise transfer characteristics by using insulation covers. However, these approaches have negative effects, such as deterioration in fuel economy and increase in cost/weight. Therefore, modification of engine structures is required to reduce it.
We analyzed noise transfer paths from a piston, a connecting rod, a crank shaft to an engine block and vibration behavior during engine operation experimentally, and identified that piston resonance was a noise source. In order to absorb resonant energies caused by vertical movement of the piston, we have designed new piston-pin structure integrated with dynamic damper which resonates in the opposite phase to the piston. We verified the diesel knock reduction by using this new technology.
